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Understanding WLANs in plain English. |
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Simple clarification of |
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Wireless broadband technologies |
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For everyone else! |
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In these chapters you will learn: |
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1 What
are WLANs |
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2 Site
Topography |
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3 Site
Surveys |
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4 FCC
regulation |
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5
Security Issues |
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LAN
Defined |
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LAN's (local area networks) are a collection of
computers connected together by wires and typically located within a few
meters of one another. Computers on a wired LAN share information and
typically can not be more than 300 meters apart. |
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WLAN
Defined |
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WLAN's (wireless local area networks) eliminate
the wires that connect computers together. There are many benefits to this
including rapid deployment of large networks, lower installation costs,
free roaming, and dramatically increased range between computers on the
WLAN.
Up to 25 miles! |
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It is
radio technology that make WLAN's possible. There is really nothing new
about wireless. When you hear the word "wireless", the first
thing that should come to mind is "radio". |
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AM &
FM, cellphones, television, and now the transfer of data are all based on
the same wireless technology invented by Guglielom Marconi over a hundred
years ago. A technology Marconi called radio. Most radio transmissions that
we typically think of are one way. Usually from a transmitter to a receiver
such as in AM & FM broadcasts. |
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WLAN's transmit data in both directions similar
to your cellphone or pair of walkie talkies. Transceivers! |
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The use
of radio technology to transfer data across a WLAN isn't quite as simple as
using a walkie talkie, but the principal is the same. |
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Cisco
engineers have developed ways to improve reliability, speeds and ranges of
WLAN's. By eliminating the wire, Cisco wireless (radio) products can now
bridge computer systems as far apart as 25 miles. With attainable speeds of
up to 11Mbps, Cisco/Aironet wireless systems are up to 5.5 times faster
than a T1. |
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A true "broadband" or "big
pipe" technology without the wire. |
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There are three main applications for WLAN's |
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1) Bridges:
Building to building
2) Access Points: In building
and campus
3) ISP‘s: Internet service
providers |
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The most popular usage of WLAN technology is
within a building or facility, providing traditional LAN topology with out
the need for wires. We use Access
Points to accomplish this application of 802.11b (Wi-Fi). |
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Free roaming capabilities where laptop computers
may travel connected from room to room are the most obvious application of
WLAN's, but often WLAN's are implemented because of the easy and speed in
which the system can be changed. |
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Other uses include railroad, airline, police and
emergency services. Aironet
wireless products control ethernet time clocks at remote locations, check
and manage flow control at water treatment plants and are mounted on
forklifts and barcode readers. |
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A new
application for WLAN technology is the wireless ISP. Cisco Aironet wireless
products are being used to deliver broadband Internet access to customers.
As a wireless ISP, you can provide faster access to the Internet than
anything available through a traditionally wired network provider. |
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Data
throughput speeds of up to ten times faster than a T1, 20 times faster than
DSL & Cable, and an amazing 1000 times faster than the fastest modems
are possible with wireless broadband technologies from Cisco Aironet. |
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In this chapter you will learn about: |
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Line of Sight (LOS) |
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Non-Line of Sight (NLOS) |
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Range |
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Speed |
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Site Surveys |
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Installation |
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Cisco frowns on marketing its 802.11b (Wi-Fi)
products for anything other than "line of sight" (LOS)
applications because it's easily deployed, reliable, and a safe way to
market 802.11b products. |
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No one is ever disappointed if 802.11b actually
works in a "non-line of sight" (NLOS) situation. The product can be used this way but it
is considered an experimental application of the technology. |
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Cisco keeps returns to a minimum by only
promoting and supporting Aironet as a LOS product. There is no
support directly available from Cisco for other, NLOS applications. |
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See “NLOS: Supported” for unusual or
experimental applications. |
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Definition of "line of sight" (LOS) |
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The ability to visually see an antenna visibly
from the other. The definition of
LOS must also include the “invisible” fresnel zone. |
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Definition of "fresnel zone“ |
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The invisible cone of the radiation emitted from
the antenna. Usually a few meters in height and calculated into the
“visible” line of site for a total area of clear space defined as “line of
site” (LOS). |
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Tip: The greater the distance, the more
vulnerable the system will be to NLOS issues. |
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Definition of “Non-Line of Sight” (NLOS) |
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Any obstruction visible within the “line of
sight” between two antennas, is considered “non-line of sight” NLOS |
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Any obstruction within the fresnel zone
constitutes “non-line of sight” NLOS |
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In this chapter you will learn about: |
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Site Surveys |
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Installation |
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Site surveys assure that a wireless system will
perform as expected, before the actual installation ever takes place. |
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A proper survey includes the following |
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Conducted on-site with wireless equipment |
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A report is generated with throughput and ranges
acquired |
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An estimate of installation time and material
costs |
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Why you shouldn't have a sight survey |
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If you have clear line of site over very short
distances. |
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If you have a long distance & an obstacle
between the antennas, it is a good reason not to do a site survey.
Stick to medium & short distances for the "experimental"
applications. The more distance you apply, the more
"experimental" you become. |
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If you are concerned about the cost of a site
survey, your project may not be large or complex enough to warrant a site
survey, but if you eliminate even one T1 connection the savings can be
significant and thus may be worth bridging your LAN's even in a NLOS
system. |
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It's always prudent to get a site survey
if you are making a investment. |
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This is especially so, if your application is
experimental (NLOS). Many wireless companies won't approach experimental
application of wireless systems. |
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Webcats Wireless Networks is currently working
with experimental NLOS applications of 802.11b (Wi-Fi). See: Chapter2 NLOS: Supported |
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Survey terms, lead times, and costs |
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Your site survey is free anywhere in the US for
LOS systems. If the survey fails you simply pay travel expenses and
walk away without having invested in inappropriate equipment. |
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Download terms of agreement |
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Install terms, lead times, and costs |
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LOS install rate is $85.00/hr for the first man
& $65.00/hr for the second man (if required). A second man is always required in ladder & tower
situations above 1 story. |
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Download terms of agreement |
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Install terms, lead times, and costs |
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In NLOS situations, the minimum goal for
throughput over any distance is always 1Mbps. We usually obtain
higher if it is possible to obtain any throughput at all. |
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NLOS surveys are always billable at $210.00/hour
total for two men. NLOS surveys always require two men because of the
nature of the "experimental" application. Travel and cell
phone charges also apply in NLOS "experimental" applications. |
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Download terms of agreement |
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In this chapter you will learn about: |
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Licensed bands |
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Non-Licensed bands |
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In this chapter you will learn about: |
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SSID’s |
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WEP |
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LEAP (Radius) |
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Service Set Identifier: |
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A unique 32-character identifier attached to the
header of packets… |
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The SSID differentiates one WLAN from another,
so all access points and all other devices attempting to connect to a
specific WLAN must use the same SSID.
A device will not be permitted to join unless it can provide the
unique SSID. Because an SSID can be
“sniffed” it does not supply any security to the network. |
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Wire Equivalent Privacy: |
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A security protocol for 802.11b wireless local
area networks |
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A wired LAN is inherently more secure than WLANs
because of LANs are somewhat protected by the physicality of a
structure.WLANs, which are over radio waves don’t have the save physical
structure ans are therefore more vulnerable to tampering, WEP aims to provide security to WLANs be
encrypting data over radio. |
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Extensible Authentication Protocol: |
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For its Aironet solution, Cisco created an
authentication scheme called LEAP. |
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Leap provides mutual authentication between
Cisco Aironet client cards and the backend Remote Service (Radius)
server. This authentication
currently provides the highest form of WLAN security |
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Notes